1. Technical Field
The present disclosure relates to a fuel cell system and, more particularly, to a fuel cell system that is designed to more effectively recycle moisture contained in fluid circulating in the fuel cell system and with orientation free functionality.
2. Description of the Related Art
Fuel cell systems are designed to generate electrical energy through an electrochemical reaction between hydrogen and oxygen. Fuel cells are classified according to fuel used into a variety of types, such as polymer electrolyte membrane fuel cells (PEMFCs), direct methanol fuel cells (DMFCs), and the like.
The PEMFCs use a hydrogen ion exchange polymer membrane as an electrolyte membrane. A fuel containing the hydrogen to electrochemically reacts with an oxidizing gas containing the oxygen therein, thereby continuously generating electrical energy and heat. The PEMFCs typically exhibit excellent output characteristics compared with other types of fuel cells, and have lower operational temperatures. In addition, the PEMFCs start and respond quickly relative to other types of fuel cells. Fuel cell systems using the PEMFC have been used in a variety of applications, such as portable power sources or battery-alternative power sources. The fuel cell systems are generally designed to supply the oxidizing gas and fuel to each fuel cell stack.
In DMFCs, a liquefied fuel such as methanol is directly supplied to each fuel cell stack without using a fuel reformer. The DMFCs receive the liquefied fuel and air, and generate electrical energy through an oxidation reaction of the fuel and a reduction reaction of the oxidizing gas therein. Fuel cell systems using DMFCs typically have relatively simple structures, and thus have been used as portable power sources and small-sized power sources.
In the above-described fuel cell systems, after the fuel electrochemically reacts with the oxidizing gas, unreacted fuel and carbon dioxide (CO2) are discharged through an anode outlet, and unreacted oxidizing gas and water are discharged through a cathode outlet. In order to recycle the unreacted fuel, the carbon dioxide is separately discharged and the unreacted fuel is recycled to the fuel cell stack. Further, the unreacted oxidizing gas is separately discharged and the water (moisture) generated by the electrochemical reaction is mixed with the unreacted fuel and supplied to the fuel cell stack.
In the fuel cell system, the moisture generated by the electrochemical reaction is discharged through the cathode outlet mixed with the unreacted oxidizing gas. Therefore, in order to recycle the water (moisture), a typical fuel cell system includes a fluid recycling apparatus for separating the moisture from the oxidizing gas. The fluid recycling apparatus cools the unreacted oxidizing gas discharged from the fuel cell stack to a predetermined temperature or less to condense the moisture contained in the oxidizing gas into liquid water so that the moisture and the oxidizing gas can be separated from each other by gravity.
When a fuel cell system having, for example, a DMFC is used as a portable or small-sized power source, the fluid recycling apparatus may shake or rotate. As a result, the water separated from the unreacted oxidizing gas may remix with the unreacted oxidizing gas, or leak out of the fuel cell system. This type of problem is generally expressed as “a low orientation free performance.” That is, since the typical fuel cell system has a low orientation free performance, the power efficiency of the typical fuel cell system is reduced.